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To allow anything to depend on WASI types, including platform-specific data structures, move the WASI libc filesystem/clock interface into `platform_api_extension.h`, which leaves just WASI types in `platform_wasi.h`. And `platform_wasi.h` has been renamed to `platform_wasi_types.h` to reflect that it only defines types now and no function declarations. Finally, these changes allow us to remove the `windows_fdflags` type which was essentially a duplicate of `__wasi_fdflags_t`.
This folder contains the platform abstract layer for multiple platforms. To support a new platform, you can simply create a new folder here and implement all the APIs defined in include folder.
Refer to port_wamr.md for how to port WAMR to a target platform.